1. Field of the Invention
This invention relates to a surgical staple and a method of and apparatus for producing such a surgical staple.
2. Prior Art
A conventional surgical staple comprises a steel wire of a circular cross-section, and has a base portion and a pair of leg portions respectively extending angularly from the opposite ends of the base portion, the distal end of each leg portion being sharp. A number of such staples are adapted to be loaded into a stapler. The stapler is operated to bend the base portion at two points disposed respectively adjacent to the pair of leg portions, so that the pair of leg portions are driven into the body of the patient on opposite sides of a wound, and at the same time are urged toward each other, thereby suturing or sewing up the wound.
There are known various types of staples. A first type of staple, as shown in FIG. 19 of Japanese Patent Publication No. 36694/87, has a straight base portion and a pair of parallel leg portions respectively extending perpendicularly from the opposite ends of the base portion. A second type of staple, as shown in FIG. 12 of Japanese Patent Publication No. 46854/82, is similar to the first type of staple, but differs in that the central portion of its base portion is bent in a direction of extending of its leg portions. A third type of staple, as shown in FIG. 31 of Japanese Patent Publication No. 37983/87, has a base portion which is so bent that the overall shape of the staple is much like a figure "3", and its leg portions are not parallel to each other but are directed outwardly away from each other. A fourth type of staple, as shown in FIG. 5 of Japanese Patent Publication No. 4535/86, is similar to the third type of staple but has a pair of leg portions directed inwardly toward each other.
In each of the above four types of staples, the axis of the base portion and the axes of the pair of leg portions are disposed in a common plane. Further, each of the leg portions has at its distal end portion only one inclined surface inclined with respect to the axis of the leg portion. This inclined surface perpendicularly intersects the above common plane, and faces outwardly, that is, away from the opposite leg portion. The inclined surface intersects the cylindrical peripheral surface of the leg portion at the distal end thereof to form a sharp edge.
The above conventional staples has a drawback. More specifically, each leg portion of the staple has the sole inclined surface, and the angle of the distal end edge is equal to the angle between the axis of the leg portion and the inclined surface. When the angle of the distal end edge is made smaller, the ability of the leg portion to penetrate into the human body is enhanced, but the strength of the distal end edge decreases. In contrast, when the angle of the distal end edge is made larger, its strength is increased, but the penetrating ability thereof decreases. Thus, it has been difficult to enhance both of them.
The inventor of the present invention has magnified and observed the inclined surface from the side thereof, with the leg portion held in a vertical condition, and has found that one of about right and left halves of the inclined surface is relatively smooth whereas the other is coarse. The present inventor has presumed from this fact that in the conventional staples, the inclined surface is formed in the following manner: Cutting edges of upper and lower blade members are disposed in parallel relation to the above common plane in which the axis of the base portion of the staple as well as the axes of the pair of leg portions is disposed, and the cutting edge of the upper blade member is moved in a direction perpendicular to the above common plane to shear each leg portion to thereby form the inclined surface. As a result, one of the right and left halves of the inclined surface defines a relatively smooth sheared surface whereas the other defines a coarse ruptured surface. With this shearing method, the staple suffers from the following drawbacks in addition to the above-mentioned drawback:
(1) When the leg portion of the staple held in a vertical condition is viewed from the side thereof, the axis of the leg portion is bent to either the right or the left in the vicinity of the distal end of the leg portion. It is thought that this arises out of the fact that the leg portion is deformed in the vicinity of its distal end when the upper blade member is moved to effect the shearing. Because of such bending of the distal end portion of the leg portion, the leg portion has a lowered penetrating ability. PA1 (2) When the distal end edge of the leg portion in which the inclined surface terminates has been magnified and observed in a direction perpendicular to the above plane, the distal end edge assumes a relatively rounded configuration. It is thought that this arises out of the fact that the distal end edge is curled on the upper blade member when the leg portion is sheared. This results in a lowered penetrating ability of the leg portion. PA1 (3) Burrs are formed on the side edge of the leg portion defined by the ruptured surface (defining one of the right and left halves of the inclined surface) and the cylindrical peripheral surface of the leg portion. These burrs damage the flesh of the patient when the leg portion is caused to penetrate thereinto.